The intestinal Na+/H+ exchanger NHX-2 regulates both cellular pH and nutrient uptake in the nematode C. elegans, and loss-of-function leads to decreased fat stores and increased lifespan. In order to ask whether these phenotypes are mechanistically a result of altered pH or of caloric restriction, a global RNAi screen for other targets that alter intestinal cellular pH was performed. Almost a quarter of the 45 clones identified function in the mitochondria;in particular, ETC complex I was well-represented, as were proteins involved in mitochondria! ribosome function and in regulating mitochondrial morphology. Further testing suggested that several clones act at least in part cell non-autonomously. We propose here first to identify in which cells the non-autonomous functions occur using a novel system for cell specific RNAi. Then we will examine mitochondrial redox potential, pH, morphology, and energy production in vivo following RNAi in the relevant cells, as well as fat uptake and longevity in the targeted worms. Finally, we will target each clone in cultured nematode embryonic cells to directly test cell autonomy. The results of these experiments will provide mechanistic insights into how mitochondria influence intestinal cellular pH, as well as how this coupling influences fat metabolism and aging. Obesity has become a pressing health concern, particularly in younger people, over the last decade, and is one of the leading risk factors for developing diabetes and heart disease. Our research is aimed at defining how mitochondria, which meets the energy demands of the cell, influences pH homestasis in a well- conserved genetic model organism. Since cellular pH is linked to nutrient uptake, fat accumulation, and longevity, this functional coupling may represent a unique means of cellular communication and a novel target for anti-obesity therapeutics.